Oxidation number of Sulfur in FeSO4

I know oxygen is -2, so 4(-2). What is my next step?

FeSO4 charge is neutral

SO4 is 2-, oxygen is -2 each*4 = -8
Fe is 2+

You can set it up like this

S + 4(-2) = -2

S + -8 = -2
S = -2 + 8
S = 6

Charge of sulfur in FeSO4 is +6

Sulphate always has a charge of -2, so S + 4O = -2. From there, you can work out the value for S.

S + 4O = -2
S + 4(-2) = -2
S = -2 + 8
S = +6

sulfur is+6, oxygen is -2 x 4, for a net ionic charge of -2.